Cosmology Lesson 1

A careful look at the night sky shows a diversity of stars. Some are brighter than others; some are reddish, or bluish. When we study the light given off by stars, we see even more diversity.

A: Properties of Stars: We start this lesson with a look at three different ways of measuring the properties of stars.

• One measure is the color of the light from stars, which tells us the temperature of the star (red-hot stars are actually cooler than blue-hot stars!).
• Another measure is the luminosity of stars, which tells us how much light is given off by stars, whatever the color.
• Finally, the stellar mass tells us how much matter is contained in the star.

Are these properties related? Do more massive stars give off more light? Do bluish stars give off more light? This simulation gives a three-dimensional view of how the properties are related. When you study the graph there, see if you got the point by trying quiz GQ2 .

B: Stellar Radiation: How do we know all of this information about stars? Well, each of the above measurements is difficult and indirect. We can't measure the temperature of a star with a thermometer. Instead, we study the light coming from the star, and compare it with things on Earth that glow. The rainbow of light from each star has some interesting connections to the rainbow of other glowing objects. This site shows how stellar spectra can tell us about the star's temperature. After plotting ten curves at a nice range of temperatures, take a picture of the graph, overlay it on graph paper, and make a data table that links temperature with the peak of the curve. If you can find the mathematical equation that fits this pattern, you just learned Wien's Law! Finally, see if you understood the pattern in Wien's Law by trying this game !

C: Stellar Rainbows: The spectrum of light from stars is not as smooth as it appeared in the Blackbody Radiation exercise above. In fact, small "bites" are taken out of the rainbow, in the same way that parts of the sun's rainbow never make it through our atmosphere. This led to the conclusion that there is vaporized matter in stars, and these elements remove predictable parts of the spectrum. This activity shows you the spectrum with "bites" taken out of it. This site shows you the spectral signatures of different elements. The activity I1StellarRainbows in the courses folder will give you practice finding the elements contained in stars. When you are done, take the quiz here to see if your observations and logic were accurate!

To sum up, here is a presentation of ideas.

Why Aren't There Any Green Stars?